Technical Field
The inventions relate to apparatus including multi-mode optical fiber and methods to use such devices.
Discussion of the Related Art
This section introduces aspects that may be helpful to facilitating a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art.
Herein, a multi-mode optical fiber is an optical fiber having orthogonal optical propagating modes with different lateral light intensity profiles, i.e., different spatial intensity profiles. Often, such fibers also have optical propagating modes with different angular momentum eigenvalues.
In an optical transmission system having optical transmission span(s) of multi-mode optical fiber, imperfections in the optical transmission span(s) and/or optical couplers between said spans may lead to mixing of light carried on different optical propagating modes. That is, the optical fiber transmission line may have an effective channel matrix that is non-diagonal between various optical propagating modes with different lateral light intensity profiles. Such linear mixing or crosstalk may be separated out in an optical receiver that implements multi-input-multiple-output (MIMO) processing and/or equalization. Removing such linear mixing typically involves mixing detected light values from the different optical propagating modes, as measured at the optical receiver, over temporal intervals of the order of differential group delays between said optical propagating modes. To reduce the complexity of such equalization and/or MIMO processing it is typically desirable to keep group delays between the various optical propagating modes small.